Neuraline no longer generates/is required for chem (#8012)

# About the pull request
taken directly from #7023 

 #7249 didn't make it impossible to get


![image](https://github.com/user-attachments/assets/dc9bfc49-2fb3-4ffe-8f10-411a4637ca1b)

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# Explain why it's good for the game
neuraline very hard to get, removes the ability to get it or for it to
generate as a requirement for chems so that researchers can be happy.
# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
fix: Neuraline no longer generates in recipes, and is unobtainable from
botany.
/:cl:

code/modules/reagents/chemistry_reagents/medical.dm

@@ -188,9 +188,9 @@
 	custom_metabolism = AMOUNT_PER_TIME(1, 5 SECONDS)
 	overdose = 2
 	overdose_critical = 3
-	chemclass = CHEM_CLASS_SPECIAL
+	chemclass = CHEM_CLASS_RARE
 	properties = list(PROPERTY_NERVESTIMULATING = 5)
-	flags = REAGENT_TYPE_MEDICAL
+	flags = REAGENT_TYPE_MEDICAL | REAGENT_NO_GENERATION
 
 /datum/reagent/medical/arithrazine
 	name = "Arithrazine"